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Kuju Volcano - John Seach

Kyushu, Japan

33.08 N, 131.25 E
summit elevation 1788 m
Stratovolcanoes

Kuju volcano is located in the NE of Aso Caldera. Kuju volcano consists of many stratovolcanoes and lava domes. Two geothermal plants are located at the volcano. Kuju is considered one of the most hazardous volcanoes in Japan due to a history of block and ash flows from collapsing lava domes.

One of the most active geothermal fields around Kuju Volcano is Iwoyama, situated on the northeastern flank of Mt. Hossho, where sulfur used to be mined for 500 years.

Past and Future Eruptions at Kuju Volcano
The average eruption rate of Kuju volcano is about one order of magnitude higher than that from Unzen volcano. Eruption centers at Kuju volcano have migrated systematically eastward for the last 5000 years from Iwaigodake-Hizengajo domes (5 ka), to Danbaru cone (4-5 ka), Komekubo crater (2-4 ka), and Kurotake dome (1.6 ka). This suggests the next magmatic eruption may occur around or east of Kurotake.

1995 Eruption
A phreatic eruption occurred at Kuju volcano on 11th October 1995. A number of new vents opened on the eastern slope of Mt. Hossho, one of the domes of the Kuju complex, a few hundred meters from a pre-existing fumarolic area. A second ash eruption occurred on 18th December 1995. The eruptions were followed by thousands of earthquakes over the following 2 years. The earthquakes were horizontally concentrated north of the new vents vertically between 800 m above sea level and 1000 m below sea level. Slope distance changes indicate that an area near the top of Mt. Hossho has been deforming to the northeast.

In 2003, over 6 years after the phreatic eruption, the deflation rate at Kuju volcano was still approximately linear. The intensity of the fumaroles from new craters has tended to decrease with time. However, the total energy discharge of the fumaroles around Iwoyama is still higher than before the phreatic eruption.